feat(feed): move the Mine/Library scope toggle beside the header search box

The scope toggle used to sit at the top of the filter rail, which is buried when
the rail is collapsed/unpinned. Relocate it to the header, just right of the feed
search box — mirroring Plex's scope toggle placement — so the primary 'what am I
browsing' control is always visible.

New FeedScopeToggle adapter (SegmentedToggle over filters.scope, same as the Plex
one over its scope); rendered in Header on the feed page between the search box and
the sync chip. Removed the toggle from the Sidebar rail's now-unused `top` slot and
dropped the dead `top` prop from FilterRail. Same filters.scope field, so behaviour
is unchanged.

Verified live: the toggle sits beside the feed search and switches scope; the rail
no longer carries it.

frontend/src/components/Header.tsx

@@ -5,6 +5,7 @@ import type { Me } from "../lib/api";
 import SearchBar from "./SearchBar";
 import PlexSearchBox from "./PlexSearchBox";
 import PlexScopeToggle from "./PlexScopeToggle";
+import FeedScopeToggle from "./FeedScopeToggle";
 import SyncStatus from "./SyncStatus";
 import { useNavigation } from "./NavigationProvider";
 import { useFeedFilters, useFeedFiltersActions } from "./FeedFiltersProvider";
@@ -98,6 +99,9 @@ const Header = forwardRef<
       className="pointer-events-none absolute top-3 left-4 right-[calc(1rem+var(--sbw))] mx-auto max-w-[var(--content-mw,none)] z-chrome flex flex-wrap items-center justify-center gap-x-3 gap-y-2"
     >
       {search}
+      {/* Mine/Library scope sits right of the feed search box — relocated here from the filter sidebar
+          so the primary "what am I browsing" control is always in reach (mirrors Plex's scope toggle). */}
+      {page === "feed" && <FeedScopeToggle />}
       {/* Library scope (movie/show/both) sits right of the search box on Plex — relocated here from
           the filter sidebar (S3) so the primary "what am I browsing" control is always in reach. */}
       {page === "plex" && me.plex_enabled && <PlexScopeToggle />}